Method for producing mold for use in duplicating light diffusion sheet, light diffusion sheet and method for producing the same, and screen

ABSTRACT

A method of producing a mold for use in duplicating a light diffusion sheet is provided. The method includes a step of conducting sandblasting for blasting abrasive material from a blast gun to a surface of a mold base material to form unevenness in the surface of the mold base material, wherein the abrasive material is blasted to the surface of the mold base material at a blast angle of less than 90°.

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese PatentApplication JP 2004-027898 and JP2005-21939 filed in the Japanese PatentOffice on Feb. 4, 2004 and Jan. 28, 2005, respectively, the entirecontents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for producing a mold for usein duplicating a light diffusion sheet, a light diffusion sheet and amethod for producing the same, and a screen.

2. Description of the Related Art

In recent years, as means of presenting materials in a meeting and thelike, overhead projectors and slide projectors are widely used. Further,video projectors and moving picture film projectors using liquid crystalfor home use are being spread. A projection method in these projectorsis such that light emitted from a light source is modulated by, forexample, a transmissive liquid-crystal panel to form image light, andthe image light is projected on a screen through optics, such as a lens.

For example, a projector apparatus, which can form a color image on ascreen, includes a lighting optical system which splits a ray of lightemitted from a light source into rays of red (R) light, green (G) light,and blue (B) light and converges the individual rays of light topredetermined optical paths, a liquid-crystal panel (light valve) whichmodulates individually the light fluxes of RGB colors split by thelighting optical system, and a light combining part which combines thelight fluxes of RGB colors modulated by the liquid-crystal panel, andthe color image combined by the light combining part is magnified bymeans of a projection lens and projected on a screen.

Further, recently, there has been developed a projector apparatus of atype spatially modulating the light fluxes of RGB colors using anarrow-band three primary-color light source as a light source and usinga grating light valve (GLV) instead of the liquid-crystal panel.

In the above-mentioned projector apparatuses, a screen for projector isused for viewing the projected image. The screen for projector isroughly classified into a screen for front projector such that imagelight is projected from the front side of the screen to see thereflected light of the projected light by the screen, and a screen forrear projector such that image light is projected from the back side ofthe screen to see the transmitted light through the screen from thefront side of the screen. The screens of any types are required to haveexcellent recognizability and a large viewing angle.

For this reason, in the screens of any types, typically, a lightdiffusion sheet for scattering light is formed on the surface of thescreen, and the light diffusion sheet makes image light be uniformlydiffused and emitted from the entire effective region of the screen.

As a method for producing a light diffusion sheet, there have been amethod in which a speckel pattern, which is caused when a roughenedsurface is illuminated a coherent light flux, is formed in aphotosensitive resin to produce a light diffusion sheet (see, forexample, Japanese Patent Application Publications S53-51755 and2001-100621), a method in which a mask is prepared and burned on aphotosensitive resin to produce a light diffusion sheet, and a method inwhich the surface of a mold base material, such as a metal or a resin,is directly ground by mechanical processing to prepare a mold having afinely uneven surface formed, and the surface form of the mold istransferred to an ultraviolet curing resin or the like to produce alight diffusion sheet.

In addition, there have been a method in which a composition includingresin particles dispersed in a resin binder is applied to a transparentsubstrate to produce a light diffusion sheet, and a method in which amold having an uneven surface is prepared by subjecting a mold basematerial to sandblasting, and the surface form of the mold istransferred to an ultraviolet curing resin or the like to produce alight diffusion sheet (see, for example, Japanese Patent ApplicationPublication 2000-284106).

By the way, the light diffusion sheet is frquently required to havepropertie such that the light diffused by the light diffusion sheet isdirected to a desired range, namely, the diffusion angle in thelongitudinal direction is different from the diffusion angle in thelateral direction. In the production of the light diffusion sheet, amethod in which a speckel interference or mask paterrn is transferred toa photosensitive resin has been employed.

SUMMARY OF THE INVENTION

However, in the method in which a speckel interference or mask patternis burned on a photosensitive resin to produce a light diffusion sheet,when a plularity of light diffusion sheets are produced, a mold forduplicating a light diffusion sheet from the photosensitive resin mustbe prepared, and the exposure of the photosensitive resin requires anexposure time as long as several hours to several days per m². Further,after the exposure, a step for duplicating a light diffusion sheet usingthe photosensitive resin, a step for imparting electrical conduction, astep for electroforming, and the like are needed, and thus aconsiderably prolonged time and high cost are required in the productionof the mold for light diffusion sheet.

In the method in which a light diffusion sheet is produced using a moldprepared by mechanically grinding the surface of a mold base material,there are drawbacks in that the precision of grinding is not yetsatisfactory, the tools are damaged during the grinding, a very longtime is required for the grinding, and the facility for the grinding islarge.

On the other hand, in the method in which a light diffusion sheet isproduced using a mold prepared by sandblasting, a long time or high costis not required for the production of the mold, but the light diffusedby the light diffusion sheet produced by this method is typicallyisotropic in the longitudinal direction and in the lateral direction,and therefore it is difficult to control the diffusion angles in thelongitudinal and lateral directions so that the diffused light isdirected to a range having a rectangular form having long sides in thelateral direction or an elliptical form. This drawback is also found inthe method in which a composition including resin particles dispersed ina resin binder is applied to a transparent substrate to produce a lightdiffusion sheet.

In a screen for front projector of related art, the diffusion propertyof the screen is uniform over the entire surface, and therefore, thehigher the screen gain, the larger the difference in luminance betweenthe middle portion and the periphery portion of the screen, and hencethe image on the middle portion of the screen is bright, but the imageon the periphery portion is dim. This tendency is also seen in a screenfor rear projector.

For example, in the screen for front projector, typically, image displayis achieved by a method of forward and downward projection at an anglefrom a front projector (projection apparatus) fitted to a ceiling, or amethod of forward and upward projection at an angle from a frontprojector placed on a desk or a floor. In this case, when the screen forfront projector includes a isotropic diffusion sheet or anisotropicdiffusion sheet of related art, a drawback arises in that the maximumluminance of the image light is not directed to a viewer as shown inFIG. 17.

On the other hand, in a display including a rear projector (rearprojection apparatus) and a transmissive screen, the level of theuppermost part of the screen and the level of the line of sight of asitting viewer are the same, and therefore a drawback occurs in that theimage on the lower part of the screen is dim as shown in FIG. 18.

Accordingly, it is desirable to provide a method for producing a moldfor use in duplicating a light diffusion sheet, and/or a method forproducing a light diffusion sheet, which can produce at a low cost alight diffusion sheet having diffusion angles wherein the diffusionangle in the longitudinal direction is different from the diffusionangle in the lateral direction during light transmission or reflection,or having anisotropy in the diffusion properties in the longitudinal andlateral directions. Further, it is desirable to provide a lightdiffusion sheet produced by the method and/or a screen using the lightdiffusion sheet. The present invention is made in view of the abovedrawbacks and issues associated with the techniques of related art.

Inventors of the present application have found that the related artmethod for producing a mold for use in duplicating a light diffusionsheet using sandblasting has a drawback in the fact that abrasivematerial is blasted in the direction substantially perpendicular to thesurface of a mold base material for grinding the surface with highefficiency. That is, this method forms, in the surface of the mold basematerial, an isotropic roughness in the longitudinal and lateraldirections, and cannot produce a mold for duplicating a light diffusionsheet having diffusion angles wherein the diffusion angle in thelongitudinal direction is different from the diffusion angle in thelateral direction. For solving or alleviating the draw back, the presentinventors have carefully consider the method of blasting the abrasivematerial to the surface of the mold base material in the sandblastingand have made extensive and intensive studies on the method, therebycoming to conceive of the present invention.

Further, the inventors of the present application have found that acause of the drawback in that there is a difference in luminance betweenthe middle portion and the periphery portion of the screen resides inthat, at the middle portion of the screen, the incident angle of theprojector light is 0° and part of the reflected light having the largestquantity of light is reflected toward a viewer, whereas, at theperiphery portion of the screen, the incident angle of the projectorlight is not 0° and part of the reflected light having the largestquantity of light is reflected toward the outside of the screen, andthus only part of the reflected light having small quantity of light isreflected toward the viewer in front of the screen. The presentinventors have made extensive and intensive studies based on thesefindings obtained by the studies on the method of blasting the abrasivematerial to the surface of the mold base material in the sandblasting.Accordingly, the present embodiment is made to solve or alleviate thedrawback.

According to an embodiment of the present invention, there is provided amethod for producing a mold for use in duplicating a light diffusionsheet, the method including a step of conducting sandblasting forblasting abrasive material from a blast gun to the surface of a moldbase material to form unevenness or roughness in the surface of the moldbase material, wherein the abrasive material is blasted to the surfaceof the mold base material at a blast angle of less than 90°.

It is preferred that the sandblasting is conducted such that an anglebetween the surface of the mold base material and the blast gun iswithin a range of 0 to 60°.

According to another embodiment of the present invention, there isprovided a method for producing a light diffusion sheet, the methodincluding a step of duplicating a light diffusion sheet using a molddirectly or indirectly, wherein the method uses, as the mold forduplicating a light diffusion sheet, a mold produced by conductingsandblasting for blasting abrasive material from a blast gun to thesurface of a mold base material to form unevenness or roughness in thesurface of the mold base material, wherein the abrasive material isblasted to the surface of the mold base material at a blast angle ofless than 90°.

It is preferred that the sandblasting is conducted such that an anglebetween the surface of the mold base material and the blast gun iswithin a range of 0 to 60°.

According to another embodiment of the present invention, there isprovided a light diffusion sheet including a light diffusion surfaceobtained by transfer of roughness structure of a surface treated bysandblasting, wherein the sandblasting is conducted at a blast angle ofabrasive material of less than 90°.

According to another embodiment of the present invention, there isprovided a light diffusion sheet including a light diffusion surfacehaving a diffusion property wherein the diffusion property in thelongitudinal direction is different from the diffusion property in thelateral direction, wherein the light diffusion sheet has an axis-shiftof the maximum luminance in any one or both of the longitudinaldirection and the lateral direction, the axis-shift of the maximumluminance being detected when an angle dependency of diffused lightluminance from the diffusion surface for light emitted to the diffusionsurface at an incident angle of 0° is measured.

According to another embodiment of the present invention, there isprovided a light diffusion sheet including a light diffusion surfacehaving a diffusion property wherein the diffusion property in thelongitudinal direction is different from the diffusion property in thelateral direction, wherein, in the measurement of angle dependency ofdiffused light luminance from the diffusion surface for light emitted tothe diffusion surface at an incident angle of 0°, in any one or both ofthe longitudinal direction and the lateral direction, the maximumluminance axis is angled with respect to the normal direction of theprincipal surface of the light diffusion sheet, wherein the luminancedistribution is asymmetrical with respect to the maximum luminance axis.

According to another embodiment of the present invention, there isprovided a light diffusion sheet including a light diffusion surfacehaving a diffusion property wherein the diffusion property in thelongitudinal direction is different from the diffusion property in thelateral direction, wherein the light diffusion surface has fine surfaceelements which has raised or lowered structured, and which isasymmetrical with respect to the normal of the principal surface of thelight diffusion sheet.

It is preferred that the light diffusion surface has a roughnessstructure with a pitch of 300 μm or less.

According to another embodiment of the present invention, there isprovided a screen including a light diffusion sheet which includes alight diffusion surface having a diffusion property wherein thediffusion property in the longitudinal direction is different from thediffusion property in the lateral direction, and which has an axis-shiftof the maximum luminance in any one or both of the longitudinaldirection and the lateral direction, the axis-shift being detected bythe measurement of angle dependency of diffused light luminance from thediffusion surface for light emitted to the diffusion surface at anincident angle of 0°.

It is preferred that the axis-shift is in the direction of the middleportion of the screen.

According to another embodiment of the present invention, there isprovided a screen including: the light diffusion sheet according to anyof the embodiments described above; and a reflective layer formed on thelight diffusion sheet on the side opposite to the light diffusionsurface.

According to another embodiment of the present invention, there isprovided a screen including the light diffusion sheet according to anyof the embodiments described above, wherein the light diffusion sheettransmits light projected from the side opposite to the light diffusionsurface and diffuses and emits the light through the light diffusionsurface.

According to the embodiments of the present invention described above,the roughness can be easily formed in the surface of the mold basematerial by sandblasting with high precision wherein the form of theroughness in the longitudinal direction is different from that in thelateral direction, and a mold which can duplicate light diffusion sheetscan be produced in single operation of the sandblasting.

In addition, according to the embodiments of the present invention, byusing the mold for duplicating a light diffusion sheet, there can beeasily produced with high precision a light diffusion sheet havingdiffusion angles in such a way that the diffusion angle in thelongitudinal direction is different from the diffusion angle in thelateral direction during light transmission or reflection, or havinganisotropy in the diffusion property in the longitudinal and lateraldirections.

Further, by using the light diffusion sheet described above in a screen,light emitted from any portions of the screen can be controlled to bedirected to a desired field of view, and therefore high, uniformluminance or gain can be obtained, thus making it possible to provide ascreen having excellent recognizability.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description ofthe presently exemplary embodiment of the invention taken in conjunctionwith the accompanying drawings, in which:

FIGS. 1A and 1B are diagrammatic views illustrating sandblasting for amold base material in a method for producing a mold for use induplicating a light diffusion sheet according to an embodiment of thepresent invention;

FIG. 2 is a diagrammatic view showing the surface form of the mold forduplicating a light diffusion sheet of according to an embodiment of thepresent invention;

FIGS. 3A and 3B are diagrammatic views illustrating sandblasting for amold base material in a method for producing a mold for use induplicating a light diffusion sheet according to an embodiment of thepresent invention;

FIG. 4 is a diagrammatic view showing scanning of a blast gun in themethod for producing a mold for use in duplicating a light diffusionsheet according to an embodiment of the present invention;

FIG. 5 is a cross-sectional view showing a construction of a reflectivescreen according to an embodiment of the present invention;

FIG. 6 is a cross-sectional view showing a construction of atransmissive screen according to an embodiment of the present invention;

FIG. 7 is a photomicrograph showing the surface state of the mold forduplicating a light diffusion sheet in Example 1;

FIG. 8 is a diagram showing the surface roughness of the mold forduplicating a light diffusion sheet in Example 1;

FIGS. 9A and 9B are diagrams showing the diffusion angle of the lightdiffusion sheet in Example 2;

FIG. 10 is a diagram showing the relationship between the blast angleand the anisotropy (axis-shift angle) of the diffusion property of thelight diffusion sheet in Example 3;

FIG. 11 is a photomicrograph showing the surface state of the mold forduplicating a light diffusion sheet in Example 5;

FIGS. 12A and 12B are diagrams showing the surface roughness of the moldfor duplicating a light diffusion sheet in Example 5;

FIG. 13 is a diagram showing the frequency distributions with respect tothe angle of slope of the fine surface element of the mold forduplicating a light diffusion sheet in Example 5;

FIGS. 14A and 14B are diagrams showing the luminance distribution of thelight diffusion sheet in Example 5;

FIGS. 15A and 15B are diagrams showing the luminance distribution of thelight diffusion sheet in Example 7;

FIGS. 16A and 16B are diagrams showing the luminance distribution of thelight diffusion sheet in Example 8;

FIGS. 17A and 17B are explanatory views for luminance distribution of areflective screen of related art; and

FIG. 18 is an explanatory view for luminance distribution of atransmissive screen of related art.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinbelow, a method for producing a light diffusion sheet of accordingto an embodiment of the present invention will be described.

The method for producing a light diffusion sheet includes a step ofproducing a mold for use in duplicating a light diffusion sheet, and astep of duplicating a light diffusion sheet using the mold.

(1) Step for Producing a Mold for use in Duplicating a Light DiffusionSheet

FIG. 1 illustrates production of a mold for use in duplicating a lightdiffusion sheet, in which the surface of a mold base material 1 isprocessed by sandblasting to produce a mold for duplicating a lightdiffusion sheet.

Sandblasting is processing in which abrasive material 3 is blasted froma blast gun 2 of a sandblaster (not shown) to the surface of the moldbase material 1 so that the abrasive material 3 collides with thesurface of the mold base material 1 to form an uneven surface in themold base material 1.

The sandblaster is an apparatus which blasts the abrasive material 3from the blast gun 2 by ejecting pressurized gas such as air or nitrogento the surface of a material to be processed placed on a stage toprocess the surface of the material. In the present embodiment, the moldbase material 1 is placed on the stage and subjected to sandblastingunder the predetermined conditions shown below.

The abrasive material 3 preferably includes particles which areincluding a resin, glass, a metal, ceramic, or the like, and which arespherical, or angular, e.g., polygonal, especially preferably angularparticles. Examples of abrasive material include glass beads, zirconiaparticles, steel grits, alumina particles, and silica particles.

The abrasive material 3 preferably has an average particle size of 1 to1,000 μm, more preferably 5 to 600 μm, further preferably 5 to 50 μm.

It is preferred that the abrasive material 3 has a weight of 0.002 to 8mg per one particle.

The mold base material 1 is a sheet including a material suitable forsandblasting. This material is preferably a resin or a metal, such asaluminum, copper, or steel, especially preferably aluminum. The moldbase material 1 may have such a size that one sheet of the mold basematerial is sufficient to form a light diffusion sheet used in onescreen. In the continuous production using a mold roll, the mold rollmay have a width sufficient for the width of the light diffusion sheet.

Blasting conditions of the abrasive material 3 may be such that theblast angle (angle of depression) of the abrasive material 3 to theprincipal surface of the mold base material 1 in FIG. 1 is less than90°. Specifically, an angle θ between the surface of the mold basematerial 1 and the blast gun 2 is preferably 0 to 60°, more preferably 0to 20°, further more preferably 0 to 10°.

For example, in the present embodiment, when the abrasive material isblasted at an angle θof 10°, the pitches of grooves in the blastdirection of the the abrasive material 3 and in the directionperpendicular to the blast direction can be changed, and further thesurface roughness profile in the blast direction can be asymmetricalwith respect to the principal surface axis (normal) of the lightdiffusion sheet.

The abrasive material 3, which has collided with the mold base material1, grinds or deforms the surface of the mold base material 1 while beinglowered in energy, and then is scattered at an angle upwards from themold base material 1, but, when the abrasive material 3 is blasted underthe above-mentioned blasting conditions, the abrasive material 3collides at an angle with the mold base material 1, and therefore adifference is caused in the form of deformation due to the collisionbetween the lateral direction (X-axis direction) and the longitudinaldirection (Y-axis direction). For example, the form of deformation(recess) in the X-axis direction is longer than that in the Y-axisdirection under the conditions in FIG. 1. In other words, the surfaceroughness in the X-axis direction has a pitch longer than that of thesurface roughness in the Y-axis direction. The parameters of the surfaceroughness including the pitch can be controlled by changing theparameters of the mold base material 1, the abrasive material 3, and thesandblasting conditions (e.g., blasting conditions of the abrasivematerial 3). For example, when abrasive material having a large particlesize is used, there can be achieved surface roughness having largepitches in both the X- and Y-axis directions, and, when abrasivematerial having a larger density is used, deep grooves can be realized.

With respect to the form of the processed mold base material 1, theprocessed form in the blast direction of the the abrasive material 3 canbe controlled by changing the pressure of the pressurized air of theblast gun 2, which determines the energy during the blasting, the angleof the blast gun 2, the distance between the blast gun 2 and the moldbase material 1, the shape, density, or hardness of the abrasivematerial 3, the type of the mold base material, or the like. Theprocessed form in the direction perpendicular to the blast direction canbe controlled by changing the shape or hardness of the abrasivematerial. Further, the locus of the abrasive material 3 deforming themold base material 1 while being lowered in energy and the locus of theabrasive material 3 scattered from the mold base material 1 due to therepulsion force are not symmetrical, and hence the surface form shown inFIG. 2, which is asymmetrical with respect to the principal surface axisof the mold base material 1, can be formed.

By using the mold for duplicating a light diffusion sheet produced underthe above-mentioned blasting conditions, a light diffusion sheet havingdiffusion angles wherein the diffusion angle in the longitudinaldirection is different from the diffusion angle in the lateraldirection, or having anisotropy in the diffusion properties in thelongitudinal and lateral directions can be produced. For example, underthe blasting conditions of the abrasive material 3 in FIG. 1, thediffusion angle of the reflected light or transmitted light in theX-direction is smaller, and the the diffusion angle in the Y-directionis larger, so that the reflected light or transmitted light has adiffusion property such that a luminance peak axis-shifts to the X₁ sidein the X-direction.

Alternatively, the diffusion angle of the reflected light or transmittedlight in the X-direction may be smaller and the diffusion angle in theY-direction may be larger, and further, in the measurement of angledependency of diffused light luminance from the diffusion surface forlight emitted to the diffusion surface at an incident angle of 0°, themaximum luminance axis may be angled on the X₁ side with respect to thenormal direction of the principal surface of the light diffusion sheet,wherein the luminance distribution may be asymmetrical with respect tothe maximum luminance axis.

As the angle between the blast gun 2 and the mold base material 1 isreduced, that is, the angle θ is smaller, the slenderness ratio of thediffusion angle of the light diffusion sheet desscribed below can beincreased, and hence the effect of the anisotropy in the diffusionproperty is more remakable.

The abrasive material 3 is blasted from the blast gun 2 to the mold basematerial 1 at the angle θ with an angle width α. In other words, theabrasive material 3 collides with the mold base material at an anglewithin the range of angles β₁ to β₂. The angle width α is typicallyabout 10°.

When a smaller region of the mold base material 1 is processed, theangle width α may be reduced, or a distance L between the blast gun 2and the mold base material 1 may be reduced. When a larger region of themold base material 1 is processed, the sandblasting may be conductedwhile smoothly moving the blast gun 2 or the mold base material 1.

In the above description, the abrasive material 3 is blasted in onedirection, i.e., in the direction of the long side of the mold basematerial 1 {in the X-axis direction in FIG. 1(b)} so that the blastangle (angle of depression) of the abrasive material 3 to the principalsurface of the mold base material 1 is less than 90°, but, the abrasivematerial 3 may be blasted at the same angle of depression as the aboveblast angle of the abrasive material 3 to the principal surface of themold base material 1, and further at an angle to the principal axis onthe principal surface (plane defined by the X- and Y-axises) of the moldbase material 1.

For example, as shown in FIG. 3, the blast angle of the abrasivematerial 3 to the principal surface of the mold base material 1 is anangle θ₁ of depression {FIG. 3(a)}, and the blast gun 2 is disposed atan angle θ₂ to the X-axis. Thus, the reflected light or transmittedlight has the diffusion property such that a luminance peak axis-shiftsto the Xi side in the X-axis direction and to the Y₁ side in the Y-axisdirection.

In the present embodiment, by scanning the blast gun 2 over the moldbase material 1 while blasting the abrasive material 3 from the blastgun 2, the entire principal surface of the mold base material 1 issandblasted.

An example of scanning of the blast gun 2 is shown in FIG. 4. The blastgun 2 is moved over the mold base material 1 in one direction of theY-axis at a constantrate while blasting the abrasive material 3 from theblast gun 2, and, at a time when the region of collision of the abrasivematerial 3 reaches the almost end of the mold base material 1, the blastgun 2 is moved in the X-axis direction at a certain pitch, and thenmoved in the opposite direction of the Y-axis at a constant rate.Subsequently, each time when the region of collision of the abrasivematerial 3 reaches the almost end of the mold base material 1, the blastgun 2 is moved in the X-axis direction at a certain pitch, and then themovement in the Y-axis direction is reversed and the sandblasting iscontinued, thus forming a desired uneven surface in the entire mold basematerial 1.

It is preferred that the pitch of the movement in the X-axis directionis adjusted so that the adjacent regions of collision of the abrasivematerial 3 over lap to a certain extent and the mold base material 1 hasa collectively uneven surface. Alternatively, the region of collision ofthe abrasive material 3 may be covered with a mask so that the abrasivematerial 3 collides with the mold base material 1 only at the middleregion of the collision region.

The scanning method may be either a method in which the mold basematerial 1 is fixed and the blast gun 2 is moved, or a method in whichthe stage on which the mold base material 1 is placed is moved in theX-axis direction and the blast gun 2 is moved in the Y-axis direction.

With respect to the blasting conditions of the abrasive material 3, thescanning may be conducted so that the angle θ between the surface of themold base material 1 and the blast gun 2 is constant as shown in FIG. 1,but the angle θ may be changed depending on the position of the moldbase material 1 on the X-axis and Y-axis coordinates.

(2) Step for Duplicating a Light Diffusion Sheet

The mold for duplicating a light diffusion sheet produced in theabove-described step for producing a mold for use in duplicating a lightdiffusion sheet has a finely engraved surface having a predeterminedroughness structure. A light diffusion sheet may be produced utilizingthe finely engraved surface. Any method of producing a light diffusionsheet from the finely engraved surface, which directly or indirectlyemploys the instant mold for copying a light diffusion sheet, may beused in the present embodiment.

For example, the methods that directly employ the mold for copying alight diffusion sheet may include a method in which a light diffusionsheet is produced by press-forming process with the mold, for example,by pressing the mold against thermoforming plastic film to shape acopied light diffusion sheet. Alternatively, a desired light diffusionsheet may be obtained by applying an ultraviolet curing resin to themold and covering it with a transparent substrate, and curing the resinby irradiation of ultraviolet light and removing the cured resin fromthe mold. Further alternatively, a light diffusion sheet includingstacked cured resin layers may be produced by repeating the abovetreatment of application of the resin onto the mold and curing of theresin covered with the transparent substrate. In order to improvedemolding property of molding material from the mold, it is preferableto treat the surface of the mold for demolding with nickel evaporation,fluorinated material, silicon system material coating, etc.

The methods that indirectly employ the mold for copying a lightdiffusion sheet may include a method in which a mold for copying a lightdiffusion sheet, which is manufactured in a manufacturing step of theabove-described mold for copying a light diffusion sheet, may be made toa master, and such a master mold may be copied by producing itselectroforming mold, and then a light diffusion sheet may be copied withthe copied mold in the similar manner as that of the above-describedmethod that directly employs the mold for copying a light diffusionsheet. Alternatively, after producing an reverse-shaped electroformingmold, a transfer-copied mold may be manufactured with transparentsubstance such as non-alkali glass, which absorbs less in violet lightrange. The use of transparent mold allows to cure resin by irradiatingultraviolet light from the side of the mold when a copy of the lightdiffusion sheet is made with ultraviolet resin curing.

It is preferred that the ultraviolet curing resin used has opticaltransparency. A variety of resins, such as acrylic resins, polyesterresins, polyvinyl chloride, polyurethane, and silicone resins, may beused, but there is no particular limitation. An ultra violet absorberfor preventing the cured resin from suffering degradation due toultraviolet light irradiation can be added in a slight amount, or alight absorber can be added in the application which needs coloring.

In addition, as the material constituting the light diffusion sheet, athermoformable plastic or radiation curing resin containing fineparticles for controlling the refractive index of the sheet can be used,and examples of fine particles to be added include oxides of Ti, Zr, Al,Ce, Sn, La, In, Y, Sb, or the like, and alloy oxides of In-Sn or thelike. When Ti oxide contains an appropriate amount of an oxide of Al,Zr, or the like for suppressing the photocatalytic action, the effect ofthe present embodiment is not sacrificed.

The fine particles preferably have a specific surface area of 55 to 85m²/g, more preferably 75 to 85 m²/g. When the specific surface area ofthe fine particles falls in this range, a dispersion treatment for thefine particles enables the fine particles to have a particle size of 100nm or less in the material for optical film, thus making it possible toobtain an optical film having a very small haze.

A dispersant for dispersing the fine particles is added in an amount of3.2 to 9.6×10¹¹ mol/m², based on the fine particles, and, when theamount of the dispersant is smaller than this range, satisfactorydispersibility of the particles in the light diffusion sheet cannot beobtained. On the other hand, when the amount of the dispersant is largerthan this range, the volume ratio of the dispersant to the coated filmis increased to lower the refractive index of the film, so that therange of the refractive index which can be employed becomes narrow, thusmaking it difficult to design the light diffusion sheet.

The amount of the polar functional group which is a hydrophilic groupcontained in the dispersant is 10⁻³ to 10⁻¹ mol/g. When the amount ofthe functional group is smaller or larger than this range, an effect inrespect of dispersion of the fine particles is not exhibited, leading toa lowering of the dispersibility.

The functional groups shown below are effective polar functional groupssince they cause no aggregation:

-   -   —SO₃M, —OSO₃M, —COOM, P═O(OM)₂ (wherein M represents a hydrogen        atom or an alkali metal, such as lithium, potassium, or sodium),        tertiary amines, and quaternary ammonium salts    -   R₁(R₂) (R₃)NHX (wherein each of R₁, R₂, and R₃ represents a        hydrogen atom or a hydrocarbon group, and X-represents an ion of        halogen element, such as chlorine, bromine, or iodine, or an        inorganic or organic ion)    -   —OH, —SH, —CN, an epoxy group, etc.        With respect to the site into which the polar functional group        is introduced, there is no particular limitation. These        dispersants can be used individually or in combination.

In the present embodiment, the amount of the dispersant (or the totalamount of the dispersants) in the coated film is preferably 20 to 60parts by weight, more preferably 38 to 55 parts by weight, relative to100 parts by weight of the ferromagnetic powder. With respect to thesite into which the polar functional group is introduced, there is noparticular limitation.

It is preferred that the lipophilic group in the dispersant has a weightaverage molecular weight of 110 to 3,000. When the molecular weight ofthe lipophilic group is smaller than this range, a drawback occurs inthat the dispersant is not satisfactorily dissolved in an organicsolvent. On the other hand, when the molecular weight is larger thanthis range, satisfactory dispersibility in the optical film cannot beobtained. The molecular weight of the dispersant is measured by gelpermeation chromatography (GPC).

The dispersant may have a functional group which undergoes a curingreaction, together with a binder. If the binder other than thedispersant in the present embodiment is contained, a polyfunctionalpolymer having a number of bonding groups, or a monomer is preferred.

For controlling the thickness of the light diffusion sheet, the coatingcomposition can be diluted with an organic solvent, and, for example, aketone solvent, such as acetone, methyl ethyl ketone, methyl isobutylketone, or cyclohexanone; an alcohol solvent, such as methanol, ethanol,propanol, butanol, or isobutyl alcohol; or an ester solvent, such asmethyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyllactate, or ethylene glycol acetate may be used. These organic solventsneed not have a purity as high as 100%, and they may contain animpurity, such as an isomer, an unreacted substance, a decompositionproduct, an oxide, or moisture, in an amount of 20% or less. Forapplying the coating composition onto the substrate having low surfaceenergy, it is desired to select a solvent having a lower surfacetension, and examples of such solvents include methyl isobutyl ketone,methanol, and ethanol.

Examples of binders, which undergo a curing reaction together with thedispersant, include thermosetting resins, ultraviolet (UV) curingresins, and electron beam (EB) curing resins. Examples of thermosettingresins, UV curing resins, and EB curing resins include polystyreneresins, styrene copolymers, polycarbonate, phenolic resins, epoxyresins, polyester resins, polyurethane resins, urea resins, melamineresins, polyamine resins, and urea-formaldehyde resins. A polymer havinganother cyclic (aromatic, heterocyclic, or alicyclic) group may be used.Alternatively, a resin having in its carbon chain fluorine or a silanolgroup may be used.

A method of advancing the curing reaction of the resin may be any one ofirradiation and heat, but, when the curing reaction of the resin isadvanced by irradiation of ultraviolet light, it is preferred that thereaction is carried out in the presence of a polymerization initiator.Examples of radical polymerization initiators include azo initiators,such as 2,2′-azobisisobutyronitrile and2,2′-azobis(2,4-dimethylvaleronitrile); and peroxide initiators, such asbenzoyl peroxide, lauryl peroxide, and t-butyl peroctoate. The amount ofthe initiator used is preferably 0.2 to 10 parts by weight, morepreferably 0.5 to 5 parts by weight, relative to 100 parts by weight ofthe sum of the polymerizable monomers.

The transparent substrate may be any material which satisfies desiredoptical properties, for example, a transparent film including a polymer,such as polyethylene terephthalate (PET), polyethylene naphthalate(PEN), polyether sulfone (PES), or polyolefin (PO), a glass plate, anacrylic plate, a methacryl styrene plate, a polycarbonate plate, or afluorine resin. It is preferred that the material constituting thetransparent substrate has optical properties such that the refractiveindex is 1.3 to 1.6, the haze is 8% or less, and the light transmittanceis 80% or more. The transparent substrate may have an anti-glarefunction.

The light diffusion sheet of the present embodiment includes a lightdiffusion surface obtained by transfer of a surface form of the moldproduced by the above method, the light diffusion surface having thediffusion property wherein the diffusion property in the longitudinaldirection is different from the diffusion property in the lateraldirection, wherein the light diffusion sheet has an axis-shift of themaximum luminance in any one or both of the longitudinal direction andthe lateral direction, the axis-shift being detected by the measurementof angle dependency of diffused light luminance from the diffusionsurface for light emitted to the diffusion surface at an incident angleof 0°.

Alternatively, the light diffusion sheet of the present embodiment mayinclude a light diffusion surface obtained by transfer of a surface formof the mold produced by the above method, the light diffusion surfacehaving the diffusion property wherein the diffusion property in thelongitudinal direction are different from the diffusion property in thelateral direction, wherein, in the measurement of angle dependency ofdiffused light luminance from the diffusion surface for light emitted tothe diffusion surface at an incident angle of 0°, in any one or both ofthe longitudinal direction and the lateral direction, the maximumluminance axis is angled with respect to the normal direction of theprincipal surface of the light diffusion sheet, wherein the luminancedistribution is asymmetrical with respect to the maximum luminance axis.

Further, the light diffusion sheet of the present embodiment includes alight diffusion surface including a plurality of fine surface elementshaving raised or lowered structures, and having the diffusion propertywherein the diffusion property in the longitudinal direction isdifferent from the diffusion property in the lateral direction, whereinthe light diffusion surface has fine surface elements which has raisedor lowered structure, and which is asymmetrical with respect to thenormal of the principal surface of the light diffusion sheet.

A reflective screen is described as a screen according to an embodimentof the present invention.

FIG. 5 is a cross-sectional view showing the construction of areflective screen of the present embodiment.

The reflective screen of the present embodiment includes a lightdiffusion sheet 14 according to the embodiments of the presentembodiment, and a reflective layer formed on the light diffusion sheet14 on the side opposite to the light diffusion surface, and has aconstruction such that, for example, as shown in FIG. 5, an opticalmultilayer film 12, a light absorbing layer 13, and the light diffusionsheet 14 are formed on a substrate 11.

The substrate 11 may be including any material which satisfies desiredoptical properties, for example, a transparent film, a glass plate, anacrylic plate, a methacryl styrene plate, a polycarbonate plate, a lens,or a fluorine resin. It is preferred that the material constituting thesubstrate 11 has optical properties such that the refractive index is1.3 to 1.6, the haze is 8% or less, and the light transmittance is 80%or more. The substrate 11 may have an anti-glare function.

The optical multilayer film 12 includes an optical film 12H having ahigh refractive index obtained by applying a coating composition H foroptical film described below and curing it, and an optical film 12Lhaving a low refractive index obtained by applying a coating compositionL for optical film described below and curing it wherein the opticalfilm 12H and the optical film 12L are alternately stacked on oneanother. Specifically, the optical multilayer film 12 has a constructionsuch that the optical film 12H is first formed on the substrate, andthen the optical film 12L is formed thereon, and subsequently theoptical film 12H and the optical film 12L are alternately formed, andfinally the optical film 12H is formed, and it is preferred that theoptical multilayer film 12 is a stacked film including (2n+1) layers(wherein n is an integer of 1 or more).

The optical film 12H is an optical film formed by applying the coatingcomposition H for optical film onto the substrate 11 or optical film 12Land then effecting a curing reaction for the composition.

This optical film preferably has a thickness of 80 nm to 15 μm, morepreferably 600 to 1,000 nm. When the thickness of the optical film islarger than 15 μm, the amount of a haze component including theundispersed fine particles is increased, making it difficult to achievean appropriate function of the optical film.

The optical film preferably has a refractive index of 1.6 to 2.1. Whenthe refractive index of the optical film is higher than 2.1, thedispersion property of the fine particles is unsatisfactory, so that thefunction of the optical film deteriorates, and, when the refractiveindex is lower than 1.6, the required optical properties are frequentlynot obtained.

The optical film 12L is a fluorine-containing film or silica or hollowfine particles-containing film formed by applying the coatingcomposition L for optical film onto the optical film 12H and theneffecting a curing reaction for the composition.

The optical film 12L especially preferably has a refractive index of1.45 or less. The refractive index of the optical film 12L is determineddepending on the type of the resin contained in the coating compositionand optionally the type and amount of the fine particles.

This optical film preferably has a thickness of 80 nm to 15 μm, morepreferably 600 to 1,000 nm.

By virtue of having the above-described construction, the opticalmultilayer film has high reflection properties with respect to light inthree wavelength regions, i.e., red, green, and blue light, and has hightransmission properties with respect to at least visible light inwavelength regions other than the three wavelength regions. By changingthe refractive index or thickness of each of the optical film 12H andthe optical film 12L, the wavelength in the three wavelength regions tobe reflected by the optical multilayer film can be shifted andcontrolled, so that the optical multilayer film can appropriately dealwith the wavelength of the light emitted from a projector.

With respect to the number of layers of the optical film 12H and opticalfilm 12L constituting the optical multilayer film, there is noparticular limitation, and the optical films 12H, 12L may have a desirednumber of layers. It is preferred that the optical multilayer filmincludes an odd number of layers so that the outermost layer on each ofthe projector light incident side and the opposite side includes theoptical film 12H. The optical multilayer film including an odd number oflayers has a more excellent function of a filter for the wavelengthregions of the three primary colors than that of an optical multilayerfilm including an even number of layers.

Specifically, it is preferred that the optical multilayer film includesan odd number of layers in the range of 3 to 7 layers. When the numberof layers is 2 or less, the optical multilayer film unsatisfactorilyfunctions as a reflective layer. On the other hand, the larger thenumber of layers constituting the optical multilayer film, the higherthe reflectance of the optical multilayer film, but, when the number oflayers is 8 or more, the increase rate of the reflectance is small, andthe effect of improving the reflectance expected by increasing the timefor forming the optical multilayer film cannot be obtained.

The light absorbing layer 13 absorbs the light which has passed throughthe optical multilayer film 12, and, for example, in FIG. 5, the lightabsorbing layer 13 is formed by applying a black coating composition tothe surface of the substrate 11 on the side opposite to the surface onwhich the optical multilayer film 12 is formed. Alternatively, a blackfilm may be stacked on the surface.

The light diffusion sheet 14 is obtained by the above-described methodfor producing a light diffusion sheet, and formed by stacking on theoptical multilayer film 12.

Here, an example of the optical multilayer film 12 which is awavelength-selecting type reflective layer is shown as a reflectivelayer, but the reflective layer is not limited to this in the presentembodiment, and may be any reflective layer which can reflect the imagelight. Examples include reflective layers using a material having a highreflectance over the wide range of wavelengths of visible light, such asaluminum or silver.

In the reflective screen 10, light emitted from any portions of thescreen can be controlled to be directed to a desired field of view, andtherefore uniform and high luminance or gain can be obtained, making itpossible to provide screen having excellent recognizability or mucheasier to recognize.

The screen suppresses surface scattering of the incident light on thescreen, and makes possible selective reflection such that the light in aspecific wavelength from a projector is reflected and incident light onthe screen in wavelength regions other than the specific wavelength,e.g., ambient light is transmitted and absorbed, lowering the blacklevel of an image on the reflective screen 10 to achieve high contrast,thus allowing an image with high contrast to appear on the screen evenin a brightly lit room. For example, when light from an RGB lightsource, such as a grating light valve projector using a grating lightvalve (GLV), is projected to the screen 10, an excellent image with highcontrast free from an adverse effect of ambient light can be seen at alarge viewing angle.

Specifically, the incident light to the reflective screen 10 passesthrough the optically functional diffusion sheet 11 without beingscattered at the surface of the diffusion sheet, and reaches the opticalmultilayer film 12, and the optical multilayer film 12 transmits theambient light component contained in the incident light, which isabsorbed by the light absorbing layer 14, and only the light in aspecific wavelength region responsible for the image is selectivelyreflected, and the reflected light is diffused by the surface of theoptically functional diffusion sheet 11 and sent to a viewer as imagelight at a large viewing angle. Therefore, the adverse effect of ambientlight on image light which is the reflected light can be removed almostcompletely, making it possible to achieve even higher contrast than thecontrast obtained by a screen of related art.

Here, an explanation is made on the materials H and L for optical film,which are coating compositions for forming the optical film 12H andoptical film 12L.

(1) Material H for Optical Film

The coating composition H for optical film contains fine particles, anorganic solvent, a binder which absorbs energy to undergo a curingreaction, and a dispersant.

The fine particles are fine particles including a high refractive-indexmaterial added for controlling the refractive index of the optical filmformed, and examples include oxides of Ti, Zr, Al, Ce, Sn, La, In, Y,Sb, or the like, and alloy oxides of In-Sn or the like. When Ti oxidecontains an appropriate amount of an oxide of Al, Zr, or the like forsuppressing the photocatalytic action, the effect of the presentembodiment is not sacrificed.

The fine particles preferably have a specific surface area of 55 to 85m²/g, more preferably 75 to 85 m²/g. When the specific surface area ofthe fine particles falls in this range, a dispersion treatment for thefine particles enables the fine particles to have a particle size of 100nm or less in the material for optical film, thus making it possible toobtain an optical film having a very small haze.

A dispersant for dispersing the fine particles is added in an amount of3.2 to 9.6×10¹¹ mol/m², based on the fine particles, and, when theamount of the dispersant is smaller than this range, satisfactorydispersibility of the particles in the optical film cannot be obtained.On the other hand, when the amount of the dispersant is larger than thisrange, the volume ratio of the dispersant to the coated film isincreased to lower the refractive index of the film, so that the rangeof the refractive index which can be employed becomes narrow, thusmaking it difficult to design the optical film lamination.

The amount of the polar functional group which is a hydrophilic groupcontained in the dispersant is 10⁻³ to 10⁻¹ mol/g. When the amount ofthe functional group is smaller or larger than this range, an effect inrespect of dispersion of the fine particles is not exhibited, leading toa lowering of the dispersibility.

The functional groups shown below are effective polar functional groupssince they cause no aggregation:

-   -   —SO₃M, —OSO₃M, —COOM, P═O(OM)₂ (wherein M represents a hydrogen        atom or an alkali metal, such as lithium, potassium, or sodium),        tertiary amines, and quaternary ammonium salts    -   R₁(R₂) (R₃)NHX (wherein each of R₁, R₂, and R₃ represents a        hydrogen atom or a hydrocarbon group, and X¹ represents an ion        of halogen element, such as chlorine, bromine, or iodine, or an        inorganic or organic ion)    -   —OH, —SH, —CN, an epoxy group, etc.        With respect to the site into which the polar functional group        is introduced, there is no particular limitation. These        dispersants can be used individually or in combination.

In the present embodiment, the amount of the dispersant (or the totalamount of the dispersants) in the coated film is preferably 20 to 60parts by weight, more preferably 38 to 55 parts by weight, relative to100 parts by weight of the ferromagnetic powder. With respect to thesite into which the polar functional group is introduced, there is noparticular limitation.

It is preferred that the lipophilic group in the dispersant has a weightaverage molecular weight of 110 to 3,000. When the molecular weight ofthe lipophilic group is smaller than this range, a drawback occurs inthat the dispersant is not satisfactorily dissolved in an organicsolvent. On the other hand, when the molecular weight is larger thanthis range, satisfactory dispersibility in the optical film cannot beobtained. The molecular weight of the dispersant is measured by gelpermeation chromatography (GPC).

The dispersant may have a functional group which undergoes a curingreaction, together with a binder. When the binder other than thedispersant in the present embodiment is contained, a polyfunctionalpolymer having a number of bonding groups, or a monomer is preferred.

As the organic solvent, for example, a ketone solvent, such as acetone,methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanone; analcohol solvent, such as methanol, ethanol, propanol, butanol, orisobutyl alcohol; or an ester solvent, such as methyl acetate, ethylacetate, butyl acetate, propyl acetate, ethyl lactate, or ethyleneglycol acetate may be used. These organic solvents need not have apurity as high as 100%, and they may contain an impurity, such as anisomer, an unreacted substance, a decomposition product, an oxide, ormoisture, in an amount of 20% or less. For applying the coatingcomposition onto the substrate or optical film having low surfaceenergy, it is desired to select a solvent having a lower surfacetension, and examples of such solvents include methyl isobutyl ketone,methanol, and ethanol.

Examples of binders, which undergo a curing reaction together with thedispersant, include thermosetting resins, ultraviolet (UV) curingresins, and electron beam (EB) curing resins. Examples of thermosettingresins, UV curing resins, and EB curing resins include polystyreneresins, styrene copolymers, polycarbonate, phenolic resins, epoxyresins, polyester resins, polyurethane resins, urea resins, melamineresins, polyamine resins, and urea-formaldehyde resins. A polymer havinganother cyclic (aromatic, heterocyclic, or alicyclic) group may be used.Alternatively, a resin having in its carbon chain fluorine or a silanolgroup may be used.

A method of advancing the curing reaction of the resin may be any one ofirradiation and heat, but, when the curing reaction of the resin isadvanced by irradiation of ultraviolet light, it is preferred that thereaction is carried out in the presence of a polymerization initiator.Examples of radical polymerization initiators include azo initiators,such as 2,2′-azobisisobutyronitrile and2,2′-azobis(2,4-dimethylvaleronitrile); and peroxide initiators, such asbenzoyl peroxide, lauryl peroxide, and t-butyl peroctoate. The amount ofthe initiator used is preferably 0.2 to 10 parts by weight, morepreferably 0.5 to 5 parts by weight, relative to 100 parts by weight ofthe sum of the polymerizable monomers.

The material H for optical film is applied and then dried to form anoptical film 22H in an uncured state, and then a curing reaction for thefilm is promoted by irradiation or heat in the curing step to form anoptical film 12H of a high refractive-index type.

(2) Material L for Optical Film

The coating composition L for optical film contains an organic solventand a binder. The binder is dissolved in the organic solvent and, ifnecessary, fine particles maybe added to and dispersed in the solutionof the binder.

The binder is a resin having in its molecule a functional group whichundergoes a curing reaction by irradiation of ultraviolet light or thelike or energy from heat, and especially preferred is a fluorine resinfrom the viewpoint of facilitating the removal from the release film. Itis preferred to use a polymer having a main chain modified withfluorine, a polymer having a side chain modified with fluorine, or amonomer having fluorine.

Examples of polymers having a main chain modified with fluorine includeperfluoro main chain-type perfluoropolyether, perfluoro side chain-typeperfluoropolyether, alcohol-modified perfluoropolyether, andisocyanate-modified perfluoropolyether, and examples of monomers havingfluorine include CF₂═CF₂, CH₂═CF₂, and CF₂═CHF. A polymer obtained bypolymerizing or block-polymerizing these monomers can be used.

As examples of polymers having a side chain modified with fluorine,there can be mentioned solvent-soluble polymers having a main chaingraft-polymerized, and, as an especially preferred example of the lowrefractive-index thermoplastic polymer, there can be mentionedpolyvinylidene fluoride since it can be handled with ease as a resinwhich can use a solvent. When polyvinylidene fluoride is used as the lowrefractive-index thermoplastic polymer, the resultant lowrefractive-index layer has a refractive index of about 1.4, and, forfurther lowering the refractive index of the low refractive-index layer,a low refractive-index acrylate, such as trifluoroethyl acrylate, may beadded in an amount of 10 to 300 parts by weight, preferably 100 to 200parts by weight, relative to 100 parts by weight of an ionizationradiation curing resin.

The fine particles are fine particles including a low refractive-indexmaterial optionally added for controlling the refractive index of theoptical film formed, and preferred are ultra-fine particles including amaterial, such as LiF (refractive index: 1.4), MgF₂ (refractive index:1.4), 3NaF.AlF₃ (refractive index: 1.4), AlF₃ (refractive index: 1.4),or SiO_(x)(1.5≦x≦2.0)(refractive index: 1.35 to 1.48). Hollow fineparticles may be contained.

As the organic solvent, for example, ketone solvents, such as acetone,methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; alcoholsolvents, such as methanol, ethanol, propanol, butanol, and isobutylalcohol; ester solvents, such as methyl acetate, ethyl acetate, butylacetate, propyl acetate, ethyl lactate, and ethylene glycol acetate;fluorine-containing solvents, such as fluorine-containing aromatichydrocarbons, e.g., perfluorobenzene, pentafluorobenzene,1,3-bis(trifluoromethyl)benzene, and 1,4-bis(trifluoromethyl)benzene,fluorine-containing alkylamines, e.g., perfluorotributylamine andperfluorotripropylamine, fluorine-containing aliphatic hydrocarbons,e.g., perfluorohexane, perfluorooctane, perfluorodecane,perfluorododecane, perfluoro-2,7-dimethyloctane,1,3-dichloro-1,1,2,2,3-pentafluoropropane,1H-1,1-dichloroperfluoropropane, 1H-1,3-dichloroperfluoropropane,1H-perfluorobutane, 2H,3H-perfluoropentane,3H,4H-perfluoro-2-methylpentane, 2H,3H-perfluoro-2-methylpentane,perfluoro-1,2-dimethylhexane, perfluoro-1,3-dimethylhexane,1H-perfluorohexane, 1H,1H,1H,2H,2H-perfluorohexane,1H,1H,1H,2H,2H-perfluorooctane, 1H-perfluorooctane, 1H-perfluorodecane,and 1H,1H,1H,2H,2H-perfluorodecane, fluorine-containing alicyclichydrocarbons, e.g., perfluorodecalin, perfluorocyclohexane, andperfluoro-1,3,5-trimethylcyclohexane, and fluorine-containing ethers,e.g., perfluoro-2-butyltetrahydrofuran, and fluorine-containing lowmolecular-weight polyethers, can be used individually or in combination.These organic solvents need not have a purity as high as 100%, and theymay contain an impurity, such as an isomer, an unreacted substance, adecomposition product, an oxide, or moisture, in an amount of 20% orless.

The material L for optical film is applied and then dried to form anoptical film 22L in an uncured state, and then a curing reaction for thefilm is promoted by irradiation or heat in the curing step to form anoptical film 12L of a low refractive-index type.

Next, a method for producing a reflective screen 10 according to anembodiment of the present invention is described below.

(s1) A polyethylene terephthalate (PET) film is prepared as a substrate11, and a coating composition H for optical film is applied in apredetermined amount to the principal surface of the substrate 11.

(s2) The film of the coating composition H for optical film is dried,and then cured by irradiation of ultraviolet light to form an opticalfilm 12H having a predetermined thickness.

(s3) Then, a coating composition L for optical film is applied in apredetermined amount to the optical film 12H.

(s4) The resultant film is dried, and then cured by heat to form anoptical film 12L having a predetermined thickness, thus forming astacked structure including the optical film 12H and the optical film12L.

(s5) Then, the coating composition H for optical film is applied in apredetermined amount to the optical film 12L constituting the outermostlayer of the substrate 11.

(s6) The film of the coating composition H for optical film is dried,and then cured by irradiation of ultraviolet light to form an opticalfilm 12H having a predetermined thickness. Subsequently, a cycle oftreatments in the steps s3 to s6 is repeated predetermined times to forman optical multilayer film 12 on the substrate 11.

(s7) A low refractive-index, transparent bonding agent (EPOTEK396;manufactured and sold by EPOXY TECHNOLOGY) is applied to the surface ofthe outermost layer of the optical multilayer film 12, and a lightdiffusion sheet 14 is placed on the bonding agent applied so that thesurface of the light diffusion sheet 14 on the side opposite to theuneven surface is in contact with the bonding agent, and then thebonding agent is cured so as to serve as a bonding layer for bonding theoptical multilayer film 12 to the light diffusion sheet 14.

(s8) A resin containing a black light absorber is applied to the backsurface of the substrate 11 to form a light absorbing layer 13, thusobtaining a reflective screen 10 of the present embodiment.

Next, a transmissive screen is descried as a screen according to anotherembodiment of the present invention.

FIG. 6 is a cross-sectional view showing the construction of atransmissive screen of the present embodiment. The transmissive screenof the present embodiment includes the light diffusion sheet of thepresent embodiment, wherein the light diffusion sheet transmits lightprojected from the side opposite to the light diffusion surface anddiffuses and emits the light through the light diffusion surface, forexample, as shown in FIG. 6, the transmissive screen includes a lightdiffusion sheet 102 on a substrate 101.

The substrate 101 is a substrate for transmissive screen, and can beconstituted by a polymer, such as polyethylene terephthalate (PET),polyethylene naphthalate (PEN), polymethyl methacrylate (PMMA),polyether sulfone (PES), or polyolefin (PO). When the substrate is usedin a transmissive screen, the screen incorporated into a display must beself-supporting, and therefore it is desired that the substrate 101 is atransparent material having a thickness of 0.2 mm or more and havingrigidity.

The light diffusion sheet 102 is obtained by the above-described methodfor producing a light diffusion sheet, and scatters the light which haspassed through the substrate 101 to obtain scattered light. A viewer cansee a natural image by observing the scattered reflected light.

For example, the transmissive screen of the present embodiment and atransmissive screen using a light diffusion sheet of related art suchthat the maximum luminance is in the normal direction and the diffusionproperty is symmetrical with respect to the maximum luminance axis aredisposed side by side, and image light is projected to each screen fromthe back side to observe the image from the front side of the screen. Asa result, in the display using the transmissive screen of related art,the upper part of the image is bright and the lower part of the image isdim, whereas, in the display using the transmissive screen of thepresent embodiment, a bright image having a high luminance over theentire screen can be obtained.

The diffusion property is preferably controlled by adjusting the surfaceform of the light diffusion sheet 102 per position of the screen so thatthe collective luminance distribution observed by a viewer becomesuniform over the screen. For achieving this, for example, the axis-shiftin the luminance peak is preferably directed to the middle portion ofthe screen. Specifically, with respect to the collective diffusionproperty on the entire screen, the diffusion property on the wholeperiphery portion of the screen preferably have a feature such that aluminance peak of the transmitted light is at an angle in the directionof the middle portion of the screen and the angle is continuouslyincreased in the direction of from the middle portion to the peripheryportion of the screen.

The transmissive screen 100 of the present embodiment is produced bystacking the light diffusion sheet 102 on one surface of the substrate101 including, e.g., a PET film.

The application of the light diffusion sheet of the present embodimentis not limited to the projection type display, but the light diffusionsheet can be applied to various fields, such as displays and lightingapparatuses, which need to control the viewing angle. For example, whena light source cannot be disposed on the back or front side due to therestriction on the arrangement of the light source, the use of the lightdiffusion sheet produced by the present embodiment enables light focusin a desired direction. In addition, in the application of lightingapparatus, by disposing a lighting having the light diffusion sheetproduced by the present embodiment at the corner of a room, the middleportion of the room is lit, achieving a lighting effect.

The present invention will be further described with reference to thefollowing Examples. The following Examples are merely examples, and thepresent invention is not limited to the following Examples.

EXAMPLE 1

A mold for use in duplicating a light diffusion sheet 10 was producedunder the following conditions.

(1) Mold base material: Aluminum sheet (X: 200 mm×Y: 100 mm)

(2) Sandblasting conditions

-   -   Sandblaster {model: SGF-4 (A); manufactured and sold by Fuji        Manufacturing Co., Ltd.}    -   Grit: Alumina (#180; average particle size: 76 μm)    -   Distance between the blast gun and the mold base material: 50 mm    -   Angle between the blast gun and the mold base material: 8°    -   Compressed air pressure: 0.5 MPa    -   Blasting conditions of the abrasive material for the surface of        the mold base material: Conditions shown in FIG. 1    -   Blast gun scanning conditions: Scanned at a pitch of 5 mm in the        X-direction and in the Y-direction as shown in FIG. 4.

The surface state of the mold obtained is shown in FIG. 7. There wasobserved a state such that there was a difference in the roughnessstructure of the surface between the. longitudinal direction and thelateral direction (the X-axis direction and the Y-axis direction) andthe form of deformation (recess) in the X-axis direction was longer thanthat in the Y-axis direction.

Next, the results of the measurement of surface roughness of the moldare shown in FIG. 8. A pitch Px of the surface roughness in the X-axisdirection was longer than a pitch Py of the surface roughness in theY-axis direction. An average the roughness space Sm was as follows:X-axis direction: S=0.14; and Y-axis direction: S=0.08.

EXAMPLE 2

Next, a transparent resin (PET-G film, DIAFIX; manufactured and sold byMitsubishi Plastics, Inc.) was pressed by means of the mold in Example 1to produce a light diffusion sheet.

The light diffusion sheet obtained was permitted to transmit collimatedrays of light from the back surface of the sheet to measure a diffusionangle of the transmitted light from the front side of the sheet. Theresults are shown in FIG. 9.

The light diffusion sheet exhibited diffusion angles Wherein thediffusion angle in the lateral direction (X-axis direction) is differentfrom the diffusion angle in the longitudinal direction (Y-axisdirection), and a luminance half band width in the X-axis direction was18° and that in the Y-axis direction was 45°.

In the luminance distribution in the X-axis direction {FIG. 9(a)}, aluminance peak A axis-shifts from the angle (0°) in the directionperpendicular to the light diffusion sheet. This corresponds to theanisotropy (axis-shift) of the diffusion property in the presentembodiment.

EXAMPLE 3

For determining the relationship between the angle (blast angle) betweenthe blast gun and the mold base material and the anisotropy (axis-shiftangle) of the diffusion property, molds for duplicating a lightdiffusion sheet were produced under substantially the same conditions asthose in Example 1 except that the angle (blast angle) between the blastgun and the mold base material was changed stepwise from 2 to 90°. Then,light diffusion sheets were individually produced using the molds underthe same conditions as those in Example 2, and each of the lightdiffusion sheets obtained was permitted to transmit collimated rays oflight from the back surface of the sheet to measure the luminancedistribution in the X-axis direction of the transmitted light from thefront side of the sheet.

From the luminance distribution obtained, the relationship between theblast angle and the anisotropy (axis-shift angle) of the diffusionproperty was determined. The results are shown in Table 1 below and FIG.10. Axis-shift at a predetermined angle in the blasting direction (thedirection of X₁ in FIG. 1) could be realized by adjusting the blastangle. TABLE 1 Anisotropy Blast angle (°) (axis-shift angle) (°) 2 9.510 4.8 20 3.7 30 2.5 40 1.8 50 1.1 60 0.8 70 0.05 80 0 90 0

EXAMPLE

Next, a reflective screen was produced using the following coatingcomposition H for optical film and coating composition L for opticalfilm.

(1) Coating Composition H for Optical Film Fine particles: TiO₂ fineparticles 100 Parts by weight (2.02 Wt %) (manufactured and sold byIshihara Sangyo Kaisha Ltd.; average particle size: about 20 nm;refractive index: 2.48) Dispersant: SO₃Na Group- 20 Parts by weight(0.40 Wt %) containing molecule (weight average molecular weight: 1,000;SO₃Na group concentration: 2 × 10⁻³ mol/g) Binder: Mixture of 30 Partsby weight (0.61 Wt %) dipentaerythritol hexaacrylate anddipentaerythritol pentaacrylate (UV curing resin, trade name: DPHA;manufactured and sold by Nippon Kayaku Co., Ltd.) Organic solvent:Methyl isobutyl 4,800 Parts by weight (96.97 Wt %) ketone (MIBK)

First, the fine particles, dispersant, and organic solvent inrespectively predetermined amounts were mixed together, and dispersed bymean of a paint shaker to obtain a TiO₂ fine-particle dispersion. Then,a binder was added to the dispersion and agitated by means of anagitator to prepare a coating composition H.

(2) Coating Composition L for Optical Film

Polymer of perfluorobutenyl vinyl ether having a carboxyl group at theterminal (trade name: CYTOP; manufactured and sold by Asahi Glass Co.,Ltd.)

(3) Method for Producing a Reflective Screen

(s11) The coating composition H is applied to both surfaces of atransparent substrate by a dipping method.

(s12) The films of the coating composition H are dried at 80° C., andthen cured by irradiation of ultraviolet light (UV) (1,000 mJ/cm²) toform optical films H each having a thickness of 780 nm and a refractiveindex of 1.94.

(s13) Then, the coating composition L is applied to each highrefractive-index optical film H by a dipping method.

(s14) The films of the coating composition L are dried at 90° C. to formoptical films L each having a thickness of 1,240 nm and a refractiveindex of 1.34.

(s15) The coating composition H is applied to each optical film L underthe same conditions as those in the step s11.

(s16) The films of the coating composition H are formed under the sameconditions as those in the step s12 to form optical films H each havinga thickness of 780 nm and a refractive index of 1.94, thus obtainingoptical multilayer films each including three layers, i.e., optical filmH/optical film L/optical film H per one surface, that is, six layers intotal on a transparent substrate.

(s17) The light diffusion sheet in Example 3 is stacked through anadhesive layer on the surface of one of the above optical multilayerfilms.

(s18) A black coating composition is applied to the surface of anotherof the optical multilayer films by a spraying method to form a blacklight-absorbing layer, thus obtaining a reflective screen.

Image light was projected to the reflective screen obtained to observethe image from the front of the screen. As a result, an image withuniform and high luminance could be seen at a specific site, confirmingthat the reflected image light was controlled to be directed to aspecific field of view.

EXAMPLE 5

A mold for use in duplicating a light diffusion sheet was produced underthe following conditions.

(1) Mold base material: Aluminum sheet (X: 200 mm×Y: 100 mm)

(2) Sandblasting conditions

-   -   Sandblaster {model: SGF-4 (A); manufactured and sold by Fuji        Manufacturing Co., Ltd.)    -   Grit: Alumina (#220)    -   Distance between the blast gun and the mold base material: 50 mm    -   Angle between the blast gun and the mold base material: 10°    -   Compressed air pressure: 0.5 MPa    -   Blasting conditions of the abrasive material for the surface of        the mold base material: Conditions shown in FIG. 1    -   Blast gun scanning conditions: Scanned at a pitch of 5 mm in the        X-direction and in the Y-direction as shown in FIG. 4.

The surface state of the mold obtained is shown in FIG. 11. There wasobserved a state such that there was a difference in the roughness ofthe surface between the longitudinal direction and the lateral direction(the X-axis direction and the Y-axis direction) and the form ofdeformation (recess) in the X-axis direction is longer than that in theY-axis direction.

Next, the results of the measurement of surface roughness of the moldusing a stylus-type profile meter ET4000A (manufactured and sold byKabushiki-kaisha Kosaka Laboratory) are shown in FIG. 12. A pitch Px ofthe surface roughness in the X-axis direction was longer than a pitch Pyof the surface roughness in the Y-axis direction, and an averageunevenness gap Sm was as follows: X-axis direction: S=90 μm; and Y-axisdirection: S=45 μm. In addition, it has been found that the form of thelowered portion in the Y-axis direction is symmetrical, but the form ofthe lowered portion in the X-axis direction is asymmetrical. Histogramsof the angles of slope in the X- and Y-directions of the fine surfaceelement based on the form of the cross-section in FIG. 12 are shown inFIG. 13. It has been found that the distribution of the angle of slopeof the cross-section in the X-direction is such symmetrical that it isclose to a Gaussian distribution, but the distribution of the angle ofslope of the cross-section in the Y-direction has two peaks on both thepositive and negative sides and the form of the distribution isasymmetrical (which is not a Gaussian distribution).

Next, as a substrate having a width sufficient to form a large-sizelight diffusion sheet having a high light transmittance, a PET film(thickness: 100 μm) was prepared. Then, an urethane acrylic resin havinga refractive index of 1.53 was applied to the mold, and covered with thePET film having a thickness of 100 μm while preventing the resin fromcontaining air bubbles, and then pressed by means of a rubber rollerwhile adjusting the pressure of the rubber roller so that the thicknessof the resin became uniform and 50 μm. Subsequently, the resin wasirradiated from the side of the PET film with ultraviolet light at theintegrated quantity of light of 1,000 mJ, which is sufficient topolymerize and cure the resin, and then removed from the mold, togetherwith the substrate, to transfer the surface form of the mold to theresin, thus producing a light diffusion sheet.

For examining the diffusing power of the thus produced light diffusionsheet, an aluminum reflective sheet was stacked on the back surface ofthe light diffusion sheet obtained to produce a reflective screen, andthe front surface of the screen was illuminated collimated rays of lightusing a gonio-photometer (manufactured and sold by OPTEC CO., LTD.)while changing the angle in the X-direction and Y-direction to measure areflected light strength profile. The results are shown in FIG. 14.

The angle (half band width) in the X-direction at which the reflectionstrength is half of the maximum strength was 25°, and that in theY-direction was 37°. Reflecting the surface form of the mold shown inFIG. 12 and FIG. 13, the maximum luminance angle in the Y-direction is0° and hence the diffusion property is symmetrical, but the maximumluminance angle in the X-direction is 2°, that is, the maximum luminanceis at an angle to the normal direction (direction of the normal withrespect to the principal surface of the light diffusion sheet), and theratio between the angles at which the diffused light strength is half is1.1:1 and thus asymmetrical with respect to the maximum luminance axis(axis directed from the origin to the maximum luminance peak),indicating that more light is diffused in the direction of the maximumluminance axis.

Next, an aluminum reflective sheet was stacked on the back surface of alight diffusion sheet of related art, in which the maximum luminance isin the normal direction and the diffusion property is symmetrical withrespect to the maximum luminance axis, to produce a reflective screenfor comparison. This screen and the reflective screen in the presentExample were disposed side by side, and image light was projected toeach screen to observe the image from the front side of the screen. As aresult, in the screen for comparison, the image on the middle portion ofthe screen was bright, but the image on the periphery portion was dim.By contrast, in the reflective screen in the present Example, a brightimage having a high luminance could be obtained.

Further, by disposing the reflective screen upside down, the reflectivescreen in the present Example could be used in both the forward anddownward projection at an angle from a projector fitted to a ceiling andthe forward and upward projection at an angle from a projector placed ona desk.

EXAMPLE 6

An urethane acrylic resin having a refractive index of 1.53 was appliedto a mold, which is the same mold for copying the light diffusion sheetas in the Example 5. Subsequently, the mold is covered with a PET film.The PET film serves as a supporting member, has a thickness of 100 μmand a high transparent ratio in violet light region, and one side ofwhich is subjected to easy-adhesion treatment. The mold is covered withthe PET film in such a way that the other side of surface of the PETfilm, in which no easy-adhesion treatment is performed, faces to themold surface while preventing the resin from containing air bubbles, andthen pressed by means of a rubber roller while adjusting the pressure ofthe rubber roller so that the thickness of the resin became uniform and100 μm. Subsequently, the resin was irradiated from the side of the PETfilm with ultraviolet light at the integrated quantity of light of 1,000mJ, which is sufficient to polymerize and cure the resin, to produce asheet of the resin. After the supporting member (PET film) is removed,the resin sheet is removed from the mold, thereby completing the copyingof a light diffusion sheet to which the surface structure of the mold istransferred.

For examining the diffusing power of the thus produced light diffusionsheet, an aluminum reflective sheet was stacked on the back surface ofthe light diffusion sheet obtained to produce a reflective screen, andthe front surface of the screen was illuminated with collimated rays oflight using a gonio-photometer (manufactured and sold by OPTEC CO.,LTD.) while changing the light incident angle in the X-direction andY-direction to measure a reflected light strength profile.

In the result, the angle (half band width) in the X-direction at whichthe reflection strength is half of the maximum strength was 25°, andthat in the Y-direction was 37°. The maximum luminance angle in theX-direction is 2°, that is, the maximum luminance is inclined to thenormal direction (direction of the normal with respect to the principalsurface of the light diffusion sheet). Accordingly, in the presentexample, the similar performance is obtained as in the Example 5.Furthermore, according to the present example, it was possible to obtaina bright image with a high luminance similarly as in the Example 5 whenimage light is projected on the screen and monitored near the front ofthe screen. Furthermore, in the present example, it was possible toappropriately adjust the reflective screen in both cases of settingenvironment, which include a case of projecting slant downward whenplacing a projector on a ceiling and a case of projecting slant upwardwhen placing a projector on a desk, by turning the setting direction ofthe reflective screen upside down.

EXAMPLE 7

A light diffusion sheet was produced according to the followingprocedure.

(S21) An urethane acrylic resin having a refractive index of 1.53 wasapplied to the surface of the mold produced in Example 5, and coveredwith a polyethylene terephthalate film having a thickness of 100 μmwhile preventing the resin from containing air bubbles, and then pressedby means of a rubber roller while adjusting the pressure of the rubberroller so that the thickness of the resin became uniform and 50 μm.Subsequently, the resin was irradiated from the side of the PET filmwith ultraviolet light at the integrated quantity of light of 1,000 mJ,which is sufficient to polymerize and cure the resin, and then removedfrom the mold, together with the substrate, to transfer the surface formof the mold to the resin, thus producing a light diffusion sheet A.(S22) Further, a fluorine acrylic resin having a refractive index of1.38 was applied to the same mold, and covered with the light diffusionsheet A produced in the above step, and then pressed by means of arubber roller while adjusting the pressure of the rubber roller so thatthe thickness of the resin became uniform and 30 μm. Subsequently, theresin was irradiated from the side of the PET film with ultravioletlight at the integrated quantity of light of 1,000 mJ, which issufficient to polymerize and cure the resin, and then removed from themold, together with the substrate, to transfer the surface form of themold to the resin.

(S23) Further, the steps S21 and S22 were repeated to produce a lightdiffusion sheet including four layers respectively having refractiveindexes of 1.53, 1.38, 1.53, and 1.38 in this order from the side of thePET film.

For examining the diffusing power of the thus produced light diffusionsheet, an aluminum reflective sheet was stacked on the back surface ofthe light diffusion sheet obtained, and the front surface of the lightdiffusion sheet was illuminated collimated rays of light using agoniophotometer (manufactured and sold by OPTEC CO., LTD.) whilechanging the angle in the X-direction and Y-direction to measure areflected light strength profile. The results are shown in FIG. 15.

The maximum luminance angle in the Y-direction is 0° and hence thediffusion property is symmetrical, but the maximum luminance angle inthe X-direction is 2.5°, that is, the maximum luminance is angled to thenormal direction, and the ratio between the angles at which the diffusedlight strength is half is 1.2 :1 and thus asymmetrical with respect tothe maximum luminance axis, indicating that more light is diffused inthe direction of the maximum luminance axis.

EXAMPLE 8

Instead of the aluminum flat sheet, an aluminum roll having a diameterof 20 cm was subjected to sandblasting under the same conditions asthose in Example 1, and an urethane acrylic resin having a refractiveindex of 1.53 was applied to the mold using a roll-to-roll continuousfilm-forming machine while being covered with a polyethyleneterephthalate having a thickness of 100 μm, and the resin was irradiatedfrom the side of the polyethylene terephthalate with ultraviolet lightat the integrated quantity of light of 1,000 mJ, which is sufficient tocure the resin, and then removed from the mold to produce a lightdiffusion sheet.

For examining the diffusing power of the thus produced light diffusionsheet, an aluminum reflective sheet was stacked on the back surface ofthe light diffusion sheet obtained, and the front surface of the lightdiffusion sheet was illuminated collimated rays of light using agoniophotometer (manufactured and sold by Kabushiki-kaisha OPTEC) whilechanging the angle in the X-direction and Y-direction to measure areflected light strength profile. The results are shown in FIG. 16. Themaximum luminance angle in the Y-direction is 0° and hence the diffusionproperty is symmetrical, but the maximum luminance angle in theX-direction is 3.8°, that is, the maximum luminance is angled to thenormal direction, and the ratio between the angles at which the diffusedlight strength is half is 1.3:1 and thus asymmetrical with respect tothe maximum luminance axis, indicating that more light is diffused inthe direction of the maximum luminance axis.

Next, an aluminum reflective sheet was stacked on the back surface of alight diffusion sheet of related art, in which the maximum luminance isin the normal direction and the diffusion property is symmetrical withrespect to the maximum luminance axis, to produce a reflective screenfor comparison. This screen and the reflective screen in the presentExample were disposed side by side, and image light was projected toeach screen to observe the image from the front side of the screen. As aresult, in the screen for comparison, the image on the middle portion ofthe screen was bright, but the image on the periphery portion was dim.By contrast, in the reflective screen in the present Example, a brightimage having a high luminance could be obtained. Further, by disposingthe reflective screen upside down, the reflective screen in the presentExample could be used in both the forward and downward projection at anangle from a projector fitted to a ceiling and the forward and upwardprojection at an angle from a projector placed on a desk.

EXAMPLE 9

As a light diffusion sheet, using the light diffusion sheets in Examples5 and 8 and the light diffusion sheets of the present embodimentrespectively having degrees of asymmetry of 1.5 and 2.0 with respect tothe maximum luminance axis, an aluminum reflective sheet was stacked onthe back surface of the individual light diffusion sheets to producereflective screens. In addition, using a light diffusion sheet havingisotropic diffusion property (trade name: 125PW; manufactured and soldby Kabushiki-Kaisha Kimoto) and a light diffusion sheet havingsymmetrical, anisotropic diffusion property (trade name: LSD60*25;manufactured and sold by POC), an aluminum reflective sheet wassimilarly stacked on the back surface of the individual light diffusionsheets to produce reflective screens for comparison.

Using these reflective screens, a gain (luminance relative to theluminance obtained using a perfect diffuser) was measured in the forwardand downward projection at an angle from a projector fitted to a ceilingwith respect to each of the images on the upper, lower, and middle partsof the screen, and the results are shown in Table 2 below. In thisinstance, the asymmetrical light diffusion sheets in the Examples weredisposed so that the side having larger light converging power facedupward. The measurement was made under conditions wherein the projectorwas positioned at a distance of 5 m from the screen so that specularreflection occurred at the center of the screen. TABLE 2 Gain Lightdiffusion Degree of Axis-shift Upper part Middle of Lower part sheetasymmetry angle (°) of Screen A screen B of screen C B − A B − C Example8-1 Example 5 1.0 0.0 3.7 4.3 3.9 0.6 0.4 (asymmetrical) Example 8-2Example 7 1.0 0.0 3.5 4.1 3.8 0.6 0.3 (asymmetrical) Example 8-3Asymmetrical 1.1 2.2 3.3 3.9 3.9 0.6 0 diffusion A Example 8-4Asymmetrical 1.3 3.6 2.9 3.6 3.6 0.7 0 diffusion B Comparative Isotropic1.5 3.9 1.0 1.0 1.0 0 0 Example 8-1 diffusion Comparative symmetrical,2.0 2.9 4.0 4.8 4.0 0.8 0.8 Example 8-2 anisotropic diffusion

When using the asymmetrical light diffusion sheet of the resentembodiment, the difference between the gain at the middle of the screenand the gain at the upper part and/or lower part of the screen wassmaller than that in Comparative Example 9-2, which indicates that theuniformity of luminance was improved. This effect was remarkableespecially in the screen having a large size.

The light diffusion sheet in the present Example was joined to atransparent resin substrate including polymethyl methacrylate having athickness of 2 mm so that the sheet had rigidity to produce atransmissive screen. In a display using this transmissive screen, it hasbeen found that the uniformity of luminance is improved like thereflective screen.

EXAMPLE 10

The surface of an aluminum sheet was processed by sandblasting in thesame manner as in Example 1 to produce a mold for duplicating a lightdiffusion sheet, and light diffusion sheets were produced from anultraviolet curing resin using the mold. In this instance, in thesandblasting conditions used for producing the mold, the particle sizeof the abrasive material, the power, and the blast angle were changed sothat the pitch of surface roughness in the X-direction of the moldbecame 90 to 420 μm.

The light diffusion sheets produced were used in an image display, andan image was observed at a distance suitable for observing the imagelight to evaluate the recognizability. The recognizability was evaluatedin accordance with the following three criteria: a sharp and clear imagewas obtained (symbol: O); the resolution is satisfactory, but the screenhas glaring (symbol: Δ); and the resolution is poor and the glaring ismarked (symbol: x).

The results are shown in Table 3 below. In the observation at a distanceas small as the pitch of roughness of the light diffusion sheet can berecognized, the glaring was intense and the image was not sharp.Especially when the luminance of the image light was high, the glaringwas considerably marked. TABLE 3 Pitch of surface Distance for roughnessSheet size observation Recognizability  90 μm 30 in  60 cm ∘  90 μm 40in 120 cm ∘ 180 μm 30 in  60 cm Δ 180 μm 40 in 120 cm ∘ 180 μm 60 in 200cm ∘ 260 μm 30 in  60 cm x 260 μm 40 in 120 cm Δ 260 μm 60 in 200 cm ∘420 μm 40 in 120 cm x 420 μm 60 in 200 cm Δ 420 μm 60 in 500 cm ∘

The relationship between the visual acuity and the resolution of aviewer is represented by the following formula:Resolution (dpi)=2.54×3,438×(Visual acuity)/(Distance for observation)(cm)

Specifically, when a viewer having a visual acuity of 1.0 observes animage at a distance of 60 cm, the viewer can recognize 146 dpi (pitch:173 m), and, when the viewer observes an image at a distance of 200 cm,the viewer can recognize 44 dpi (pitch: 577 μm). Therefore, theappropriate surface roughness varies depending on the distance forobservation from the light diffusion sheet used and the visual acuity ofa viewer, but, considering the observation at a distance of about 100 to200 cm, it is desired that the surface roughness (unevenness pitch) is300 μm or less.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alterations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. A method of producing a mold for use in duplicating a light diffusionsheet, the method comprising: conducting sandblasting for blastingabrasive material from a blast gun to a surface of a mold base materialto form unevenness in the surface of the mold base material, wherein theabrasive material is blasted to the surface of the mold base material ata blast angle of less than 90°.
 2. The method of producing a mold foruse in duplicating a light diffusion sheet according to claim 1,wherein: the sandblasting is conducted such that an angle between thesurface of the mold base material and the blast gun is within a range of0 to 60°.
 3. A method of producing a light diffusion sheet, the methodincluding a step of duplicating a light diffusion sheet using a molddirectly or indirectly, wherein: the method uses, as the mold forduplicating a light diffusion sheet, a mold produced by conductingsandblasting for blasting abrasive material from a blast gun to thesurface of a mold base material to form unevenness in the surface of themold base material, wherein the abrasive material is blasted to thesurface of the mold base material at a blast angle of less than 90°. 4.The method of producing a light diffusion sheet according to claim 3,wherein: the sandblasting is conducted such that an angle between thesurface of the mold base material and the blast gun is within a range of0 to 60°.
 5. A light diffusion sheet including a light diffusion surfaceobtained by transfer of unevenness structure of a surface treated bysandblasting, wherein: the sandblasting is conducted at a blast angle ofabrasive material of less than 90°.
 6. A light diffusion sheet includinga light diffusion surface having a diffusion property wherein thediffusion property in the longitudinal direction is different from thediffusion property in the lateral direction, wherein: the lightdiffusion sheet has an axis-shift of the maximum luminance in any one orboth of the longitudinal direction and the lateral direction, theaxis-shift of the maximum luminance being detected when an angledependency of diffused light luminance from the diffusion surface forlight emitted to the diffusion surface at an incident angle of 0° ismeasured.
 7. A light diffusion sheet including a light diffusion surfacehaving a diffusion property wherein the diffusion property in thelongitudinal direction is different from the diffusion property in thelateral direction, wherein: angle dependency of diffused light luminancefrom the diffusion surface for light emitted to the diffusion surface atan incident angle of 0° is measured in such a way that, in any one orboth of the longitudinal direction and the lateral direction, themaximum luminance axis is angled with respect to a normal direction ofthe principal surface of the light diffusion sheet, wherein theluminance distribution is asymmetrical with respect to the maximumluminance axis.
 8. A light diffusion sheet including a light diffusionsurface having a diffusion property wherein the diffusion property inthe longitudinal direction is different from the diffusion property inthe lateral direction, wherein: the light diffusion surface has finesurface elements which have raised or lowered structured, and which isasymmetrical with respect to a normal direction of the principal surfaceof the light diffusion sheet.
 9. The light diffusion sheet according toclaim 8, wherein: the light diffusion surface has an unevennessstructure with a pitch of 300 μm or less.
 10. A screen comprising: alight diffusion sheet which includes a light diffusion surface having aproperty wherein the diffusion property in the longitudinal Direction isdifferent from the diffusion property in the lateral direction, andwhich has an axis-shift of the maximum luminance in any one or both ofthe longitudinal direction and the lateral direction, the axis-shiftbeing detected by a measurement of angle dependency of diffused lightluminance from the diffusion surface for light emitted to the diffusionsurface at an incident angle of 0°.
 11. The screen according to claim10, wherein: the axis-shift is in a direction of a middle portion of thescreen.
 12. A screen comprising: a light diffusion sheet according toclaim 5; and a reflective layer formed on the light diffusion sheet on aside opposite to the light diffusion surface.
 13. A screen comprising: alight diffusion sheet according to claim 5, wherein the light diffusionsheet transmits light projected from a side opposite to the lightdiffusion surface, and diffuses and emits the light through the lightdiffusion surface.
 14. A screen comprising: a light diffusion sheetaccording to claim 6; and a reflective layer formed on the lightdiffusion sheet on a side opposite to the light diffusion surface.
 15. Ascreen comprising: a light diffusion sheet according to claim 6, whereinthe light diffusion sheet transmits light projected from a side oppositeto the light diffusion surface, and diffuses and emits the light throughthe light diffusion surface.
 16. A screen comprising: a light diffusionsheet according to claim 7; and a reflective layer formed on the lightdiffusion sheet on a side opposite to the light diffusion surface.
 17. Ascreen comprising: a light diffusion sheet according to claim 7, whereinthe light diffusion sheet transmits light projected from a side oppositeto the light diffusion surface, and diffuses and emits the light throughthe light diffusion surface.
 18. A screen comprising: a light diffusionsheet according to claim 8; and a reflective layer formed on the lightdiffusion sheet on a side opposite to the light diffusion surface.
 19. Ascreen comprising: a light diffusion sheet according to claim 8, whereinthe light diffusion sheet transmits light projected from a side oppositeto the light diffusion surface, and diffuses and emits the light throughthe light diffusion surface.
 20. A screen comprising: a light diffusionsheet according to claim 9; and a reflective layer formed on the lightdiffusion sheet on a side opposite to the light diffusion surface.
 21. Ascreen comprising: a light diffusion sheet according to claim 9, whereinthe light diffusion sheet transmits light projected from a side oppositeto the light diffusion surface, and diffuses and emits the light throughthe light diffusion surface.